On the use of areal roughness parameters to assess surface quality in laser cutting of stainless steel with CO2 and fiber sources

"Laser cutting provides various advantages such as high flexibility in terms of process parameters and cut material type, as well as the possibility to obtain complex geometry in different dimensions with high precision. From industrial point of view, the two more competitive laser cutting technologies are based on the use of CO2 and active fiber sources, which produce samples visually different, with non-uniform surface and different depth of the striations. The quality assessment between the two laser systems within the industry is commonly based on standard ISO 9013; that covers several aspects of quality, the most used are the surface roughness and edge perpendicularity; however 2D profilometers adopted for measures are not able to analyze the complex 3D surface topography of the cutting edge. As a result, despite the fact that the differences are visually appreciated, measured 2D roughness values of different CO2 and fiber laser cutting conditions are very similar. Recently, a greater diffusion of 3D surface profilometry devices is present. These devices allow areal surface roughness parameters to be defined, which are potentially suitable to better quantify the laser cut quality. This work points out the use of a focus-variation microscopy to acquire 3D surfaces and evaluate analytically the surface quality of laser cut edges using areal surface roughness parameters. In particular, the purpose is to define a simple and repeatable method to identify the type of cutting process analyzed through the reconstruction of surface characteristics and quality of the cut-edge. As a case study, two stainless steel samples with the same geometry obtained with different laser sources, CO2 and active, fiber is presented. For comparison purposes the cutting conditions were fixed to represent the state of the art of respective laser cutting technologies, which actually show distinct cutting edge characteristics.